Abstract
The aim of the present slag mapping is to provide the knowledge on the mineral phase and chemical composition of hot stage and slag yard
slags. A comprehensive mapping of stainless steel slag from EAF and AOD processes, collected both from high temperature and slag yards
was carried out. Minerals of stainless steel EAF and AOD slag oriented to slag stability was investigated by using XRF, Q-XRD and SEM. The
samples were collected before the de-slagging process and from the cooled slag yard, respectively. Analysis indicated that both the high and
room temperature EAF slags consist of mainly merwinite, akermanite and spinel phases. Cr-oxide exists mainly in the (Mg, Al) spinel phase.
With boron treatment (Na2B4O7) and cooling, the AOD slags exhibit significantly different minerals between the high and cooled slags. The
major minerals of the hot AOD slag (austenitic & ferrtic steels) is γ-Ca2SiO4 (C2S), merwinite, bredigite and cuspidine, while the room
temperature austenitic AOD slags contain merwinite, bredigite and cuspidine phases. The stabilized C2S phase was found in the yard ferritic
AOD slags (C/S: ~ 2.0) after boron treatment and cooling.
Results
� It is not necessary to treat the EAF slags with borate due to its low basicity and lack of C2S. Cr-oxide is mainly distributed in the spinel phase.
� The AS AOD slags (C/S: 1.4~1.7) contain the unstable γ-C2S phase at hot stage. With borate addition and cooling, the slag yard slags change into
intact aggregates. The much higher content of merwinite and cuspidine phases in the yard slag indicates that the dissolution of MgO and CaF2 in
the C2S phase during cooling.
� The high C/S value in the FS AOD slag results in the formation of high unstable C2S phase, which need to be stabilized with boron treatment to
maintain slag intergrity.
Conclusions
Minerals characterization of stainless steel EAF
and AOD slagS.G. Huang, D. Geysen, P.T. Jones, B. BlanpainDept. of Metallurgy and Materials Engineering, K.U. Leuven, Belgium
Hot stage
Slag yard
Hot Yard
Sample Hot A Hot B Yard A Yard B
C/S 0.77 1.05 0.74 0.95
Cr2O3
Total
18.2 wt% 6.1 wt% 15.8 wt% 5.6 wt%
Spinel 76 Cr2O3 66 Cr2O3 78 Cr2O3 66 Cr2O3
Matrix 6.6 Cr2O3 2.1 Cr2O3 5.5 Cr2O3 1.8 Cr2O3
Cr-oxide distribution in the AS EAF slag
AS AOD slag
+
Na2B4O7
+
Time for
reaction
Yard slagHot slag
FS AOD slag
γ-C2S (10-60 wt%)
Merwinite (10-40 wt%)
Bredigite (20-30 wt%)
Cuspidine (14-20 wt%)
CaF2 (2-5 wt%)
MgO (2-7 wt%)
No γ or β-C2S
Merwinite (45-60 wt%)
Bredigite (12-25 wt%)
Cuspidine (25 wt%)
No CaF2
MgO (1-3 wt%)
Microstructure
Na2B4O7NoStabilizer
High β-C2SHigh γ-C2SC2S phase
β-C2S (30-65 wt%)
Bredigite (10-35 wt%)
Cuspidine (15-30 wt%)
CaF2 (0 wt%)
MgO (4-12 wt%)
γ-C2S (60-85 wt%)
Bredigite (0-21 wt%)
Cuspidine (0-3 wt%)
CaF2 (3-7 wt%)
MgO (7-15 wt%)
Phase
constitution
1.8 ~ 2.12.2~2.6C/S
Aggregate, greyPowderMorphology
Yard slagHot slagSlag
Minerals of the hot and yard FS AOD slag
Bredigite
Merwinite
Cuspidine
MgO
CaO-MgO-SiO2 isothermal section at 1600°C
C/S=1.5AS AOD
105
FS AOD
C/S=2
1600°°°°C
The authors gratefully acknowledge Aperam (former ArcelorMittal Stainless Europe) and the IWT O&O project 090594 for the financial support.
AS EAF slagChemical composition of the AS and FS EAF slag
Both the AS & FS AOD slags are in the area
where C2S phase can form. The borate
treatment is essential, especially for the FS
AOD slags. The AS AOD slag has the basicity
1.4~ 1.7. In this area, the C2S can also be
stabilized by MgO or CaF2 to form the stable
mineral phases, such as merwinite, bredigite
and cuspidine.
CaO-MgO-SiO2 isothermal section at 1600°C
C/S=1
EAF AS
105
EAF FS
C/S=1.5
Both EAF AS & FS slags are located in a single liquid
slag area at 1600 °C.
Low C/S value leads to high MgO dissolution.
* In practice also Al2O3, Cr2O3 … present)Merwinite + Akermanite + Spinel